This invention relates to a bearing assembly and more particularly to elastomeric journal bearing assemblies which are used in supporting marine propeller shafts such as in ships. Elastomeric journal bearing assemblies have been found to be particularly suited for this purpose because of their exceptional ability to withstand the harmful effects of corrosive fluids and to abrasion resulting from bits of foreign materials which are carried in suspension in the sea water or other liquids in which the shaft and journal bearing assembly operate. Such elastomeric journal bearing assemblies have been made with circumferentially spaced flat rubber surfaces because it has been found that smooth rubber lubricated with water has a very low coefficient of friction. A serious limitation to water lubricated rubber bearings is the high coefficient of friction of dry rubber during start of rotation or at very low rotation of the shaft. Attempts to overcome this have been directed to continual rotation of the shaft at a slow idle speed, however, this is not a satisfactory solution. Another attempt to solve difficult start-up is to precondition the bearings for starting by pumping water into the groove between bearings, however, it is extremely difficult to introduce water to the area between the shaft and the flat rubber surface that is in frictional contact with the shaft.
The present invention provides a new and improved elastomeric bearing assembly that has a plurality of circumferentially spaced elastomeric bearing elements or segments divided by the longitudinal spaced water groove for low friction running and with the additional feature of radially moveable plastic inserts located within the spaced elastomeric bearing elements for operational use in start up. Thus provisions are made for low friction resistance during start up by running the shaft on plastic inserts and once sufficient speed is achieved, the shaft is run on the water lubricated elastomeric elements by retracting the plastic inserts so that the shaft only contacts the circumferentially spaced elastomeric bearing elements. A modification of this structure is to make the circumferentially spaced elastomeric bearing elements radially moveable within circumferentially spaced plastic support elements whereby the propeller shaft is selectively supported by either the plastic or the elastomeric elements for rotation. A further modification is to provide a stave with moveable elastomeric bearing elements and moveable plastic bearing elements whereby the propeller shaft is selectively supported by one or the other moveable elements. With such structure there will be an effective reduction in power consumed as well as a reduction in noise generated. Further modifications use only selected bearings that have moveable inserts which are generally located on the lower portions of the bearing assembly.